Method of dye stripping



Patented Nov. 19, 1940 UNITED STATES PATENT orrlcr:

METHOD OF DYE STBII'EING David Julian Block, Wlnnetka, 111., assignor to Hobart M. Cable No Drawing. Application my 15, 1935, Serial No. 31,523

3 Claims.

' upon such vat dyes is to produce a color of less intensity or even white while in the stripping bath, but the leuco base so produced is oxidized almost immediately on contact with air, with consequent production of the original color or one approaching it.

The commonest of the vat dyes are indigo and the common indigo derivatives. The invention will be primarily discussed with reference to indigo, for the sake of simplicity, but it is not to be understood that the invention is limited thereto.

By means of this invention, the vat dyes are reduced to a substantially less colored form, and are then fixed in this form in such a manner that they are not altered in color on contact with air.

In carrying out the invention, any desired reducing. dye-stripper of the ordinary types may be employed, those dye-strippers known as the sulfur" type being most commonly employed. However, other reducing stripperssuch as zinc dust and the like may be employed. The preferred dye-stripper is set forthin my co-pending appli cation, Serial No. 737,313 filed July 24, 1934, Patent Number 2,046,317 patented July 7, 1936. This stripper comprises basic zinc sulfoxylate-formaldehyde, sodium hyposulfite and sodium bisulfite as reducing agents, and monocalclum phosphate as a catalyst. In its preferred proportions the stripper comprises:

Parts 'Monocalcium phosphate Basic zinc sulfoxylate-formaldehyde 2 Sodium hyposulfite 2 Sodium bisulfl-t 1 ter, the solid constituents being stirred slowly intov the water. The dyed fabric is then immersed in the solution, and the latter brought slowly to the boiling point with intermittent stirring. The boiling is continued for a period of about fifteen minutes, and then a daring agent is added to the solution.

The fixing agent is preferably a generator of formaldehyde. In those instances where the bath is of an acidic nature, such as is used for W001, silk and animal fabrics, it is preferred to use an acidic aldehyde generator such as trioxymethylene. ably in the ratio of about one to two percent by weight, in powderedform to the bath, and the boilingis then continued for an additional period.

of about ten minutes. Following this treatment, the fabric may be removed and the dye will not be oxidized in air.

The boiling with the formaldehyde generator is not essential, but does accelerate and improve the action. However, the fabric may be allowed to remain in contact with a warm or even cool solution containing an aldehyde with fairly satisfactoryresults. The percentages of stripper, and likewise .the percentages of the formaldehyde generator will vary widely with various dye stuffs This substance is added, prefer-- and fabrics. Normally, the range of percentage of the formaldehyde generator will be from onehalf to ten percent.

When an alkaline bath is used, as is customary with cotton goods and with certain types of vat colors such as thioindigo red, it is preferred to use an alkaline formaldehyde generator such as hexamethylene' tetramine.

The mechanism of the fixing operation is not understood. It is believed that the formaldehyde forms a stable condensation product with some reduced form of the vat dye.

The foregoing description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible, in view of the prior art.

What I claim as new and desire to secure by Letters Patent is:

1. The method of stripping an indigo dye which comprises treating the dye with reducing dye stripper of the sulfur type to produce a less colored reduced product, and heating the reduced product with formaldehyde to produce an airstable product.

2. The method of decolorizing a vat dye which comprises treating said dye with a reducing dye stripper to produce a less colored reduced form thereof, and adding to a bath containing the reduccd form formaldehyde, whereby an air-stable product is produced.

3. The method as set forth in claim the dye is an indigo derivative.

2, in which 

